Question

why i am getting runtime error in javascript at

var ClientID = document.getElementById(“ClientIDTextBox”).value;

and my code is:

<script type="text/javascript">
    var ClientID = document.getElementById("ClientIDTextBox").value;
    if (ClientID == "") {
        alert("Please enter ClientID")
      }
</script>

please help me

Answer 1

You are likely getting a runtime error because the call document.getElementById is returning null. The attempt to get the property value on null leads to an error.

Try the following instead

var element = document.getElementById('ClientIDTextBox');
if (element) {
  var ClientID = element.value;
  ...
}

The root cause though is likely that your javascript is running before the DOM is loaded and hence your element with id ClientIDTextBox is not available. Ensure your javascript runs after the DOM is loaded to prevent this problem.